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April 23, 1957 Filed June B. TOCCl-GUILBERT ETAL BACK PAD 7 14, 1955 3Sheets-Sheet 1 /0 1/ E i I 10 2! I! FlE E INVEN TORS 021m 1. 5/007 y5am: lam-awe A TTORNEY United States Patent BACK PAD Beme Tocci-Guilbertand Hosmer L. Blum, San Francisco, Califi, assignors to BerneTocci-Guilbert and Henry. Gilford Hardy, jointly asitrustees, bothof,Berkeley, Calif.

Application June14, 1955, SerialN'o; 515,328

17 Claims. (Cl. 1-197) This. invention relates. to. improvements. inbackpads for supporting abrasive discs, for rotary sanders and grinders,and, especially, to such back padsuseful in the delicate abrading andblending required in refinishing, as well as finishing decoratedsurfaces on. metallic, orother subsurfaces by means ofrotatingabrasives, which operation is known inthe trade as feathering.

The feathering operation has heretoforebeen accom-. plished. using theordinary back, pads presentlyv found in v the art, having smooth, hard,compact surfaces, supporting a disc of fine grit bonded on a cloth orother fibrous, surface. It is to be understood that most abrasive ,discscomprise a paper or cloth base to which the suitable abrasive is securedby a binder. In. thefine gritsfused in the feathering process, theabrasive disc lacks the rigidity and integrity necessary to maintain itscontact. against the back pad for optimum operation. While. thecentrifugal force of the rotation may, under certain conditions, besufiicient to bring this result about," it' is not practical to operateat motorspeeds-of more than 1,300 to 2,000 R. P. M., because the thinmounting-of the abrasive tends to slip and wrinkle at high speeds underfrictional torque. Once either of'these starts, there will be only aslight interval before the abrasive istor-nor damaged beyond furtheruse. Likewise if the abrasive disc snags on the work even slightly, itWill be in-; stantly destroyed and replacement becomes necessary.

Under these circumstances it has been found desirable upon occasion totemporarily coatthe supporting faceof the back pad with an adhesivein.orderto; secure. the abrasive disc in place. However,this:entail-s.-not:only. the extra time of coating and, applying thedisc.to,.the back pad, but the cleaning of the back pad. after. every.use, which materially shortens the life of the; back pad and; undulyextends. the; time. of ithe operation.

In addition, a new type ofabrasive; disc-has'recently. become availableunder the name. gritcloth,; Gritcloth is. generally described as anopen-weave: fabric, usually cloth or plastic, impregnated with; abrasiveand, binder so that both sides of the disc; are-- available for thefeathering or sanding operation. This product has been found to be oneof of superior characteristics, but, here again, the lack of integrityof the disc,.itself, pres vents the use which its. performance wouldotherwisefdeserve. It will be readily understoodthat it, is-nobpracti:cal to coat a back pad with an adhesive everi-. to..tem-. porarily holdthe gritcloth disc in operating position. The difficulty ofholding agritcloth disc, securely.- to, the face, of the back pad is. reflectedbythe fact that in-use, when such a disc is applied to the work, thefrictional torque abrasive di'scs,.. including gritcloth; at. high.rota.tiotial.

2,789,402 Patented Apr. 23, 1957 speeds, without danger or wrinkling. ortearing and without: the. deleterious use of temporary adhesive. means.

It is alsoan object of the. present invention to pro! vide a back padcapable. of use at substantially higher rotational speeds than possible'under present practice.

Another object: of the present invention is to provide a built-in slipclutch for holding the abrasive discs, to. counteract slippage. duetofrictional torque.

Itis still another 'object of the invention to providea back' pad witha. contact surface for. thesupport: of the abrasive, which not. onlyinsures a firm grip, but which will provide for the ventilation. andrelief. of frictional heat as well.

It: is still another object of thepresentinvention to. provide abackpad' whichwill be useful in either stands. ard" rotary sanding devicesor as. an attachment. to a feathering motor.

Itis. a further object'of the invention to provide: a: flexible backpad, laminated. throughouttis contact area, to provide any degreeofzflexibility desired for any particular operation Another-object ofthe invention is. to provide a back. pad which. is readily adaptable.for use with oscillators. providing aznutating movement, such as arereferred toinsUnited States Letters Patent Nos. 2,486,078, 2,629,990 and2,63-3;008;.

It'- isstill another OhjfiClZiOfl theinvention to provide. each and allof theselfeatures. with a quick coupling nut for retaining-theabrasivedisc or discs.

Another object is to providea backpad to securethese benefitswhileoperating'either in water or under water.

Still. another objectiis to'provide a back pad which will not.materially: increase in weight while working in' or-under water. 1

Further objects: are-toprovide a construction of maxi-. mum simplicity,economy, and ease ofassemblyand di's; assembly, also such further.objects, advantages and capa-. bilities" asiwillx' fully appear and#as'are inherently pos-: sessed=by=thedevice andttheinvention describedherein.

Theinvention-further resides in the combination, con-- struction andarrangement ofparts illustrated in the ac.- companying drawings, andwhile there. is shown therein a preferred embodimentand one variantthereof, it is toibe understoodtthatthe same; are merely illustrativeof. the inventionvandthat the inventionis capable of. modifi cation andchange. and comprehends other details of constructionwithout.departingfrom the spirit thereof or the scope. of. the appended claims.

' Referring. to the. drawings:

Figure l isiaverticalsection of the back pad of the present inventionsecured in position on an oscillator and with: an abrasive disc. securedto the face thereofready for use;

Figure. 2 is=..a-. vertical ."sectionof the back pad of the presentinvention detachedfrorn either an oscillator or the stub shaft: of amotor, without an abrasive disc, and with the quick: actingretainingmutwithdrawn to showits structure;

Figure: 31' is a;- vertic al section of aback pad of the present;invention with theretaining nut in the operative position, but withaSylphon bellows replacing and substituted for-the compressionspringshown in Figures 1 and 2.

Figure; 4 is a; ver ical. sectionof the back pad with anabrasive-discsecured to the facet hereof, where the shell isznotlsecuredtothe backup pad or pads, andwhere the quiclel'ock; pins enga g e;a;.-groovein the coupling end of the hub;.

Figured-is.a;.top;plan;view 'shjowing the quick coupling lacking means;

Eigure 6 isa'; vertical section: of. a special formof the.Presentinventiqa sn eia x-adant n n un e Wfltfil'.

Figure 7 is a vertical section showing a structure similar to that shownin Figure 4, but with a backup pad faced with nonintercellular spongerubber and especially adapted for use with and under water.

Referring now more particularly to the drawings, wherein like referencenumerals indicate like parts in the several views, the back pad of thepresent invention comprises a shell 10, which may also be referred to asa mounting flange, and is radially stepped downwardly as at 11 and 12until it terminates in the radial annular flange 14. Axially it abutsand retains within it the hollow cylindrical coupling member 15, theoutward and protruding end of which is threaded as at 16 for couplingwith an oscillator 17 or the stub shaft of a feathering motor, or agrinding motor (not shown). The coupling member 15 is retained and heldin centered position with respect to the shell by an annular ring member18 whose perimeter fits directly within the shoulder formed by the step11. By welding the ring member 18 to the shell 10, or by any othersuitable means, the mounting member is secured to the shell 10 forrotation therewith. The innermost edge of the coupling member 15 isprovided with an axial slot 20 and a turn 21 to provide a bayonet joint.

The radial flange 14 is secured to backup discs 22 and 23, which are ofvarying diameters and overlap, by means of rivets 24 or any othersuitable means. While only two backup discs 22 and 23 are shown in thedrawings, it is to be understood that these may vary in number anddiameter, depending upon the degree of flexibility or stiffness requiredin any particular back pad. One or more backup pads may be used, and,obviously, if only one backup pad were used, the diameter of backup pad22 would be extended to the full outer diameter of that shown andidentified as 23. Firmly attached to the face of the backup disc 23 is afelt pad 25 of substantial thickness, which may be treated to be eitherwaterproof or waterresistant without damage to its cushioning function.Nonintercellular sponge rubber 25a may also be used in place of the feltpad 25, and this material is especially useful where the use is to be inwater or under water. Nonintcrcellular sponge rubber is water resistantand will not soak up or hold water. Hence, it will not increase inweight due to picking up and holding water. It will be observed that theinner perimeter 26 of the pad, forming a central aperture, may berounded in profile, as at 27.

Backup discs 22 and 23 are each provided with a central aperture definedby the inner perimeter 28. Within this aperture is a pressed or stampedpressure ring 30, the inner end of which is an outwardly directed radialflange 31 which bears directly against the upper face of the backup disc22, adjacent the perimeter 28. The outer end of the pressure ring 30,which extends through the aperture, is bent inwardly to form asubstantially flat abutting surface 32 and then inwardly to form theretaining flange 33. Inwardly between the'collar 18 of the couplingmember 15 and the retaining flange 33 is compression spring 34. Spring34 constantly urges the retaining ring outperimeter of the pad 25 to theinner perimeter of the pressure ring 30. In this manner the supportingsurface 35 bridges the area between the rounded inner perimeter 27 ofthe pad 25 and the pressure ring 30 to which it is secured. The area inwhich there is no under support for the facing material 35 provides aflexing zone sufficient to accommodate the range of the compressionspring 34 from the locked position shown in Figure 1 to the releasedposition shown in Figure 2, which together illustrate the range.

' The quick acting coupler is best illustrated by reference to Figure 2.It comprises a cylindrical member 40 which isadapted to be received witha slip fit within the cylindrical coupling member 15. At its outward endit is provided with a shank 41 of reduced diameter, to which is secureda crown twist button 42 by means of a rivet 43 or any other suitablemeans. A retaining flange 44 is loosely mounted around the shank 41 witha fiber washer 45 between it and the crown twist button 42. in thismanner the crown twist button 42 may be used to rotate the cylindricalmember 40 without rotating the retaining flange 44, and vice versa. Themember 40 is provided with a radially outward extending pin 46, whichpin is intended to be guided in the slot 20 and come to rest in thebayonet joint 21. The locked position of the bayonet joint 21 representsa slight axial return so that the pin will not be jarred out of lockedposition inadvertently. It is likewise apparent that the action of thespring 34 additionally insures maintenance of the pin 46 in the lockedposition.

In placing an abrasive disc 37 on the supporting nonskid face 35, thequick coupling member is first removed. When the disc 37 is in place,the cylindrical portion 40 of the quick coupler is passed through thecentral aperture of the abrasive disc and inserted into the couplingmember 15. At the same time the member 40 is rotated by the crown twistbutton 49 so that the pin 46 will engage and travel in the axial channel20. The pressure exerted axially on the crown twist button 42 is such.that the inner face of the retaining flange 44 bears against theabrasive disc and at the end of the full travel of the pin 46 it isrotated by means of the twist button 42 in the locked position in thebayonet joint M. The locked position is shown in Figures 1 and 3 and inthis manner the abrasive disc 37 is retained in operating positionagainst the supporting face 35. it will be observed that in the lockedposition the pressure ring member 31 is moved axially inwardly againstthe action of spring 34.

wardly and axially until this movement is stopped by the flange 31abutting the upper surface of the backup disc 22. This extended positionis shown in Figure 2.

One of the important features is that the felt pad 25 or sponge rubberpad 25a is faced with piped rubber 35, or any other suitable nonskidsurface. The piped rubber 35 has been found very desirable-because themany little rubber cylinders 36 contact the abrasive disc and support itduring the sanding or feathering operation; This kind of support notonly tends to prevent any slippage of the abrasive disc thereon due tofrictional torque, but if any slippage tends to develop, the piping willgive sufficiently to dissipate any possibility of wrinkling ordistorting the surface of the disc. Likewise, the heat generated by thefrictional torque in contact with the work surface is dissipated to alarge degree through the ventilation provided by the air passages in thepiped rubber support 35. The nonskid supporting surface 35 extends fromthe outer This insures a tight grip at the central portion of theabrasive disc 37 between the pressure ring surface 32 and the retainingflange 44. It will also be observed that in the locked position, thecentral portion of the back pad is countersunk, which countersinkingextends to the curved innner perimeter 27 of the pad 25. Obviously, anydegree of countcrsinking may be obtained by the appropriate positioningof the pin 46, or otherwise.

In Figure 3 the structure shown is identical with that shown in Figures1 and 2, with the exception that a Sylphon bellows 50 has beensubstituted for the spring 34. There appear to be certain conditionswhere a Sylphon bellows-type pressure is preferable to that of thecompression spring 34.

Referring now to Figure 4, it wiil be observed that the externalcoupling portion 35a is made integral with the hub member 50. The hubmember 5% is so shaped that it conforms to the shape of the shell Iiiiaand the shoulder portion 11 which it supports. The shell ltia issecured, in any suitable manner, to the hub portion 50 for rotationtherewith. The radial flange 14a of the shell 10a terminates with anupturned flange 51 and is not secured in any way to the backup pad orpads 22 and 23. It merely supports the pad or pads 22 and 23 at theplace of contact and thus permits greater flexibility in use than if itwere secured by the rivet 24 or any, other means,

tr sses The backup pads 22 and-Zhrealso supported on theirinner sideadjacent the internalperimeter 28, by the.

face 52 of the hub member Ft). On their outer side they are held by.ring member '3, which is substantially a mere continuation of the hub 50and which is secured to the hub Why a plurality of countersunk screws54. The felt pad 25 (or nonintracellular sponge rubber pad 25a) extendsinwardly up to and abuts the ring member 53, so that the outer surfaceof the piped rubberfacing 35 continues in the same line andbecomes theouter face of the ringmember 53.

The abrasive disc 37 is shown in position on the back pad, ready foroperation.

The abrasive disc is retained in the operative position in a mannersimilar to that shown in Figures 1, 2, and 3. However, in the form shownin Figures 4, 5, 6, and 7 the cylindrical member 40a slidably moves inthe coupling portion 15:: of the hub member 50. In this instance,therefore, the cylindrical member 40a has the locking pin 46a extendingdiametrically through and projecting at both sides adjacent its outerend. Accordingly, to accomplish the axial sliding movement of thecylindrical member 40a in and out of locked position, the couplingmember 15a is provided with inwardly directed radial slots 55, whichaccommodate the outward extensions of pin 46a. In the locked positionshown in Figures 4, 5, and 6, the pin 46a has been rotatedcounterclockwise so that one projecting portion has come against stop56, whereby the pin 46a is then directed into the end groove 57 and heldthere by compression spring 62. As in the other forms, the crown twistbutton 42 is the means provided for pressing and rotating thecylindrical member 40a in and out of the locked, operative position.

The cylindrical member 46a passes through a central aperture in a deepdrawn retaining member ii'which has a diameter in the draw suificient toreceive and permit free rotation of the crown twist button 42. On thecylindrical member 40a, between an inner shoulder 53 of the couplingportion 15a and the aperture in the deep draw of the retaining member60, is a split ring 61 which acts as a stop against the shoulder forinward axial movement of the twist button and cylindrical member 40!:and against the member 60 in the released position. The cylindricalmember 40a is constantly urged toward the released position by thecompression spring 62 which bears on the inner face of the deep draw ofthe retaining member 60 and the inner face of the crown twist button 42;

The member 60 has a radial peripheral flange 63 which bears against theouter surface of an abrasive disc 37 to hold the same in operativelocked position. There are times, however, when it is desirable toinsert a rubber washer or ring 59 to bear against the abrasive disc 37and receive the wear, rather than the flange 63. It is likewise to beobserved that the retaining member 64 is free to rotate around themember 4011. This slip-clutch permits the necessary creep underrotational torque to prevent the wrinkling or tearing of the abrasivedisc.

The device shown in Figure 6 is particularly useful; for surfacing orgrinding when the same is done in or under water. The shell after thestep. 11, extends outwardly substantially to the full diameter of thepad. Nonintercellular sponge rubber 25a is secured to the shell Mb forrotation therewith. The hub 50, instead of being in two parts as inFigure 4, which includes the ring 53, is in a single unitary piece withthe coupling end a. The noninterc'ellular sponge rubber 25a will notpick up or hold water as will intercellular sponge, either natural orsynthetic, and, thus, there is no increase in the weight due to the pickup of water when working either in or under water with the device. Asthe broken lines 64 show, the member 40 1 may be made with a centralbore which acts as a through-pass for water tothe wet pad.

It is apparent that the conventional retaining nut could beused in placeof the quick acting twist lock retaining means. by. havingthe threads ofthe retaining nut shank coupling member 15.

Figure. 7 shows a unit-which has a coupling structure. similar. to thatshown in Figure 4, but has a backup disc, 23 faced with.nonintercellular sponge rubber 25a as showninEigure 6. The member 40a isalso shown with a central bore64 which is a through-pass for water,making this. particular unit. suitable and available for use withandunder water.

The present application is a continuation-in-part of our earlier filedapplication, filed April 5, 1955, under SerialNo. 499,406, nowabandoned.

We claim:

1. A back pad for abrasive discs and the like comprising a mountingshell, a coupling member for attaching to a driving means. secured foraxial rotation with said shell, abackup disc having a central openingand bearing against the periphery of said mounting shell, a ring memberoutwardly securing said backup disc to said coupling member adjacent thecentral opening for rota-v tion therewith, a retaining member having aperipheral flange for bearing against anabrasive disc and holding itagainst independent movement between said ring mem: ber and said member,said retaining member being mounted for independent slight rotationalmovement re-. sulting from frictional torque providing a slip clutch,pressure means within said shell and coupling member, passing throughand retained by said retaining member, and twist lockmeans on saidpressure means cooperating with said coupling member for quickattachment to and detachment from said coupling member.

2. A back pad for abrasive discs and the like comprising amountingshell, a coupling member for attaching to a driving means secured foraxial rotation with saidv shell, a backup disc having a central openingand bearing. against the periphery of said mounting shell, a ring memberoutwardly securing said backup disc to said coupling. member adjacentthe central opening for rotation therewith, a relatively soft padsecured to the outer surface of said backup disc, a retaining memberhaving. a peripheral flange for bearing against an abra-. sive disc andholding it against independent movement between said ring member andsaid member, said retaining member being mounted for independent slightrotational movement resulting from frictional torque providinga. slipclutch, pressure means within said shell and coupling member, passingthrough and retained by said retainingmember, and twist lock means onsaid pres-. sure means cooperating with said coupling member for quick.attachmentto and detachment from said coupling member.

3.. A back pad. for abrasive discs and the like comprising a mountingshell, a coupling member for attach+ ing to a driving, means secured foraxial rotation with said. shell, a backup disc having a central openingand bearing against the periphery of said mounting shell, a relativelysoft pad secured to the outer surface of said backup disc, a pipedrubber surface secured to the outer face of said pad, a retaining ringfor bearing against an abrasive disc and holding it against independentmovement, said retaining ringbeing mounted for independentslightrotational movement resulting from frictional torque providing aslip clutch, pressure means within said shell and coupling member,passing through and retained by said retaining ring, and twist lockmeans on said pressure means cooperating with said coupling member forquick attachment to and detachment from said coupling member.

4. A back. pad for abrasive discs and the like comprising a mountingshell, a coupling member for-attaching to adriving means secured foraxial rotation with said shell, a backup dischaving a central openingand bearing against the periphery of said mounting shell,,anonintercellular sponge rubber pad securedto the outer surface of saidbackup disc, a piped rubber surface secured to the outer face of saidpad, a retaining ring for bearing against an abrasive disc and holdingit against independent movement, said retaining ring being mounted forindependent slight rotational movement resulting from frictional torqueproviding a slip clutch, pressure means Within said shell and couplingmember, passing through and retained by said retaining ring, and twistlock means on said pressure means cooperating with said coupling memberfor quick attachment to and detachment from said coupling member.

5. A back pad for abrasive discs and the like comprising a mountingshell, a coupling member for attaching to a driving means secured foraxial rotation with said shell, a backup disc having a central openingand bearing against the periphery of said mounting shell, 9.nonintercellular sponge rubber pad secured to the outer surface of saidbackup disc, a piped rubber surface secured to the outer face of saidpad, a retaining ring for hearing against an abrasive disc and holdingit against independent movement, said retaining ring being mounted forindependent slight rotational movement resulting from frictional torqueproviding a slip clutch, a threaded retaining nut cooperating with saidcoupling member and retaining ring for securing an abrasive disc forrotation therewith.

6. A back pad for abrasive discs and the like comprising a mountingshell, a coupling member for attaching to a driving means secured foraxial rotation with said shell, a backup disc having a central openingand bearing against the periphery of said mounting shell, a relativelysoft pad secured to the outer surface of said backup disc, a pipedrubber surface secured to the outer face of said pad, a retaining ringfor bearing against an abrasive disc and holding it against independentmovement, said retaining ring being mounted for independent slightrotational movement resulting from frictional torque providing a slipclutch, a threaded retaining nut cooperatiug with said couplin memberand retaining ring for securing an abrasive disc for rotation therewith.

7. A back pad for abrasive discs comprising a mounting shell, a couplingmember for attaching to a driving means secured axially for rotationwith said shell, a backup disc having a central aperture secured to saidmounting shell, a pressure ring within said central aperture having astop thereon for limiting its outward movement, pressure means withinsaid shell and retained by said pressure ring urging the latteroutwardly, a relatively soft pad for the under surface of said backupdisc, a nonskid surface for said pad extending over the entire area fromthe perimeter and attaching centrally to the pressure ring, and a twistbayonet lock means cooperating with said coupling member to retain anabrasive disc against said nonskid surface for rotation with said backpad.

8. A back pad for abrasive discs comprising a mounting shell, a coupiingmember for attaching to a driving means secured axially for rotationwith said shell, a backup disc having a central aperture secured to saidmounting shell, a pressure ring within said central aperture having astop thereon for limiting its outward movement, pressure means withinsaid shell and retained by said pressure ring urging the latteroutwardly, a relatively soft pad for the under surface of said backupdisc, a nonskid suri for said pad extending over the entire area fromthe perimeter and attaching centrally to the pressure ring, and athreaded retaining nut cooperating with said coupling member to retainan abrasive disc against said nonskid surface for rotation with saidback pad.

ward movement, pressure means within said shell and retained by saidpressure ring urging the latter outwardly, a waterproof pad for theunder surface of said backup discs, a nonskid surface for said padextending over the entire area from the perimeter and attachingcentrally to the pressure ring, and a twist bayonet lock meanscooperating with said coupling member to retain an abrasive disc againstsaid nonskid surface for rotation with said back pad.

19. A back pad for abrasive discs comprising a mounting shell, acoupling member for attaching to a driving means secured axially forrotation with said shell, a plurality of backup discs having a centralaperture secured to said mounting shell, a pressure ring Within saidcentral aperture having a stop thereon for limiting its outwardmovement, pressure means Within said shell and retained by said pressurering urging the latter outwardly, a nonintracellular sponge rubber padfor the under surface of said backup discs, a nonskid surface for saidpad extending over the entire area from the perimeter and attachingcentrally to the pressure ring, and a twist bayonet lock meanscooperating with said coupling member to retain an abrasive disc againstsaid nonskid surface for rotation with said back pad.

ll. A back pad for abrasive discs comprising a mounting shell, acoupling member for attaching to a driving means secured axially forrotation with said shell, a plu rality of backup discs having a centralaperture secured to said mounting shell, a pressure ring Within saidcentral aperture having a stop thereon for limiting its outwardmovement, pressure means within said shell and retained by said pressurering urging the latter outwardly, a nonintracellular sponge rubber padfor the under surface of said backup discs, a piped rubber surface forsaid pad extending over the entire area from the perimeter and attachingcentrally to the pressure ring, and a twist bayonet lock meanscooperating with said coupling member to retain an abrasive disc againstsaid piped rubber surface for rotation with said back pad.

12. A back pad for abrasive discs comprising a mounting shell, acoupling member for attaching to a driving means secured axially forrotation with said shell, a plurality of backup discs having a centralaperture secured to said mounting shell, a pressure ring Within saidcentral aperture having a stop thereon for limiting its outwardmovement, pressure means within said shell and retained by said pressurering urging the latter outwardly, a nonintracellular sponge rubber padfor the under surfaces of said backup discs, a piped rubber surface forsaid pad extending over the entire area from the perimeter and attachingcentrally to the pressure ring, and a threaded retaining nut cooperatingwith said coupling member to retain an abrasive disc against said pipedrubber surface for rotation With said back pad.

13. A water resistant back pad for abrasive discs and the likecomprising a combined mounting shell and backup disc, a coupling memberfor attaching to a driving means secured for axial rotation with saidshell and having an axial bore therethrough, a nonintercellular spongerubber pad secured to the outer face of said shell and surrounding saidcoupling member, a piped rubber surface secured to the outer surface ofsaid pad, a retaining ring for holding an abrasive disc between it andsaid coupling member, pressure means Within the bore of said couplingmember retained by said retaining ring, and twist lock means on saidpressure means and cooperating with said coupling member for quickattachment and detachment from said coupling member.

14. A water resistant back pad for abrasive discs and the likecomprising a combined mounting shell and backup disc, a coupling memberfor attaching to a driving means secured for axial rotation with saidshell and having an axial bore therethrough, a nonintercellular spongerubber pad secured to the outer face of said shell and surrounding saidcoupling member, a piped rubber surface secured to the outer surface ofsaid pad, a retaining ring for holding an abrasive disc between it andsaid coupling member, pressure means within the bore of said couplingmember retained by said retaining ring having an axial boretherethrough, and twist lock means on said pressure means andcooperating with said coupling member for quick attachment anddetachment from said coupling member.

15. A water resistant back pad for abrasive discs and the likecomprising a combined mounting shell and backup disc, a coupling memberfor attaching to a driving means secured for axial rotation with saidshell and having an axial bore therethrough, a nonintercellular spongerubber pad secured to the outer face of said shell and surrounding saidcoupling member, a piped rubber surface secured to the outer surface ofsaid pad, a re taining ring for holding an abrasive disc between it andsaid coupling member, and a threaded retaining nut cooperating with saidcoupling member and retaining ring for securing an abrasive disc forrotation therewith.

16. A backing pad for an abrasive disc or the like comprising a mountingshell, a coupling member threaded for attachment to a driving means,retained for axial rotation with said shell and having an axial openingtherethrough, a backup disc having a central opening registering withsaid axial opening, the perimeter of said opening being countersunk withrespect to the plane of the disc, a relatively soft pad secured to theouter surface of said backup disc, a piped rubber facing secured to theouter surface of said pad, "a ring corresponding with said centralopening with screws therethrough for threaded engagement with saidcoupling member securing the intervening members together, and quickreleasing locking means passing through the axial opening and engagingsaid coupling member in the locked position, for holding an abrasivedisc to the piped rubber facing for rotation therewith.

17. A backing pad for an abrasive disc or the like comprising a mountingshell, a coupling member threaded for attachment to a driving means,retained for axial rotation with said shell and having an axial openingtherethrough, a backup disc having a central opening registering withsaid axial opening, the perimeter of said opening being countersunk withrespect to the plane of the disc, a relatively soft pad secured to theouter surface of said backup disc, a piped rubber facing secured to theouter surface of said pad, a ring corresponding with said centralopening with screws therethrough for threaded engagement with saidcoupling member securing the intervening members together, a resilientwasher corresponding with said central opening for bearing against theabrasive disc when in operating position, and quick releasing lockingmeans passing through the axial opening and engaging said couplingmember in the locked position, having an outward radial flange forhearing against said resilient washer for holding an abrasive disc tothe piped rubber facing for rotation therewith.

References Cited in the file of this patent UNITED STATES PATENTS1,648,663 St-ratfoi'd Nov. 8, 1927 2,402,691 Stever June 25, 19462,486,947 Hilger Nov. 1, 1949 2,501,524 Jones Mar. 25, 1950 2,556,434Mitchell June 12, 1951 2,620,605 Holford Dec. 9, 1952 FOREIGN PATENTS730,509 France Oct. 17, 1932

